How fast do fleas spread?


Fleas are highly reproductive, allowing them to multiply and spread quickly. On average, a female flea will lay 25 eggs per day. And she’ll survive for 7 days. The new eggs will reach adulthood in 17 to 26 days. Within a month, she’ll have thousands of descendants, but most won’t reach adulthood.

A majority of the eggs won’t survive, due to either being infertile, cannibalized by larvae, ingested by the grooming host, or having fallen into an uninhabitable environment. Still, assuming a dog acquires 5 female fleas, and 25% of the eggs survive, within a month the infestation would grow to over 4,000 fleas.


How Many Eggs Females Lay

On average, a female flea lays 20-30 eggs a day, or roughly an egg per hour. She’ll begin producing eggs 1-2 days after acquiring a host and consuming a blood meal.

Oviposition rates begin low, with 5-10 eggs produced on the second and third days of feeding. Egg production peaks 4-9 days after the first blood meal. At the peak, females can lay up to 46 eggs a day, but, in most cases, they deposit a maximum of 25-30 eggs per day. A high oviposition rate is sustained for 2-4 weeks before tapering off.

Adult Flea Lifespan

In natural settings, adult fleas live for around a week. Though they can survive for over 100 days, their lifespan is significantly reduced due to host grooming. Within a week, cats will groom off or ingest around 50% of their fleas. They can kill 3-12 fleas per day.


The total number of eggs a female can produce depends upon her lifespan. Older studies believed that average fecundity was close to 800 eggs. Newer research shows that an average female lays less than 200 eggs during her lifetime. It can be estimated that average fecundity is close to 175 eggs, given that females live for an average of 7 days and produce 25 eggs a day.

Most Eggs Don’t Reach Adulthood

Fertile vs Non-Viable Eggs

A large portion of laid eggs will be non-viable and can’t develop. Only 30-46% of the eggs will be fertile, depending on how many times the female has mated.

Host Grooming

Fleas lay their eggs on the host animal, but they drop off within a few hours. However, before they fall, some of the eggs will likely be ingested by the host during grooming. One study suggests the amount consumed may be as high as 27.7%.

Habitat & Food Requirements

Dislodged eggs drop into the environment. They continuously fall, getting distributed anywhere the infested host wanders. However, to survive and continue developing, the eggs must fall onto substrates with specific requirements. Viable habitats aren’t widespread around homes. However, many eggs accumulate in areas where pets habitually sleep, rest or feed. These areas are typically well suited for development.

Flea eggs require a relative humidity (RH) between 50% and 92%. And the ambient temperature must be between 50.4°F (10°C) and 100.4°F (38°C) for survival. The larvae also require dark, protected environments. They’ll avoid sunlight, moving toward shaded areas or burrowing beneath the surface.

Upon hatching, the larvae must have access to flea dirt and eggs for food. They’ll starve within 3 days without these nutritional components.


Flea larvae will feed on conspecific eggs, both fertile and non-viable. However, the may prefer non-viable eggs because of their flat, easy-to-grip shape. The larvae will also cannibalistically feed on younger or injured larvae. Late stage larvae may even consume pupae without full cocoons.

Host Availability

In a home environment, newly emerged adults must find a host and feed within a couple weeks or they’ll starve. To help ensure a host is around when they emerge, adults can remain quiescent inside their cocoons for up to 155 days. They’ll rapidly emerge once they detect a host.

Flea Life Cycle

Cat fleas are holometabolic insects. They develop through four distinct phases: Egg, larva, pupa, and adult. Infestations consist of 50-57% eggs, 34-35% larvae, 8-10% pupae, and 1-5% adults. Discovering adult fleas on a pet is only seeing the “tip of the iceberg”. For every adult, there are around 100 immature stages hidden in the environment.

How quickly fleas develop depends upon temperature and humidity. In a home environment, the life cycle often completes in 17 to 26 days. Eggs hatch into larvae within 2-3 days. Larvae begin spinning a cocoon and pupating 7-11 days after hatching. The cocooned prepupae will pupate and reach adulthood in 7-19 days.

How Fast Fleas Reproduce

Fleas are highly reproductive and multiply at a rapid rate. Within a month, a single female will breed thousands of descendants, though most won’t reach adulthood.

Let’s put together the aforementioned factors, while simplifying a bit. Let’s assume a dog acquires 5 female fleas. Each flea lays 25 eggs a day. Of those 125 eggs, 75% are either non-viable, cannibalized, consumed by the host, or fall into inhospitable environments. This leaves around 30 viable eggs per day. With an average life of 7 days, these 5 females will lay a total of 210 eggs that’ll eventually reach adulthood.

Now let’s assume it takes 20 days for the eggs to become adults, and half will be female. At day 20, 15 new females will emerge, jump onto the host, feed, mate, and begin laying a total of 90 viable eggs per day. At day 21, another 15 females will emerge and do the same. And so on. The flea population will grow exponentially. By day 30, the infestation in the home would surpass 4,400 fleas. And as time goes on, it will continue to exponentially increase.

The longer a flea problem goes undetected and untreated, the worse it will become, which will lead to difficulties in control. Oftentimes pet owners don’t realize how bad an infestation truly is, because 95-99% of the flea population is hidden in carpets as eggs, larvae, and pupae.


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